The invention relates to a laser diffraction particle size analyzer, particularly, a particle size analyzer capable of measuring fine particles.
In a general laser diffraction particle size analyzer, a laser beam is irradiated on particles in a scattered state, and a spatial intensity distribution of diffracted and scattered light is measured. The result is converted into a particle size distribution through Mie's scattering theory or Franhofer's diffraction theory (for example, refer to Japanese Patent Publication (Kokai) No. 06-241975). In such a laser diffraction particle size analyzer, a visible laser beam is used for irradiating on particles as the laser beam (for example, refer to Japanese Patent Publication (Kokai) No. 2001-33376). A photodiode array such as a ring detector detects the diffracted and scattered light from the particles (refer to Japanese Patent Publication (Kokai) No. 06-241975).
Incidentally, in such a particle size analyzer, it has been known that a lower limit of particle diameter in measuring a particle size distribution depends on a wavelength of laser beam irradiated on the particles. Accordingly, when the laser beam has a shorter wavelength, it is possible to measure particles with smaller diameters. In the conventional laser diffraction particle size analyzer, the visible laser beam is used, thereby restricting the lower limit of particle diameter in measuring a particle size distribution.
In view of the problem described above, the present invention has been made, and an object of the invention is to provide a particle size analyzer capable of measuring particles with diameters smaller than that the conventional laser diffraction particle size analyzer can measure.
Further objects and advantages of the invention will be apparent from the following description of the invention.